1. Field of the Invention
The present invention relates to water-dispersible polyester blends. More specifically, the invention relates to blends of polymers of .alpha.,.beta.-unsaturated monomers polymerized in the presence of sulfonate-containing polymers such that intimate blends of the polymers are achieved.
2. Discussion of the Background
There is a continuing interest in novel polymer blends or polyblends which are mixtures of structurally different homopolymers, copolymers, terpolymers and the like. Polyblends may be prepared from a wide variety of copolymers and terpolymers including random, alternating, graft and block copolymers, and terpolymers. Polyblend properties are generally a combination of the properties of the known polymer components of the polyblend and thereby exhibit new and useful polymer properties.
Polyester polyblends are known and are generally prepared by melt blending. However, intimate blends of water-dispersible polyesters are generally difficult to prepare because of the high melt viscosities of the polyesters involved and the incompatibility of most polyester polymers with other polymers. Additionally, intimate polyblends are very difficult to disperse in water if either of the polymers is not water dispersible or water soluble.
Blends can also be prepared in solution followed by removal of solvent, but this approach also has inherent problems. A mutual solvent or solvent mixture must be found that maintains compatibility as the polymer concentration increases during solvent removal. Frequently, two polymers are compatible at low concentrations in a solvent, but phase separation will occur as the solvent is removed. Furthermore, solvent removal is a difficult and expensive process, and even small amounts of solvent will create problems during further thermal processing of the polymer blend.
The formation of one polymer in the presence of another polymer is a known concept. For example, "core/shell" polymer systems are known in which a crosslinked "core" is first polymerized by emulsion polymerization, followed by addition of a second monomer which is polymerized to form a "shell."
Nonionic water-soluble polymers including poly(vinyl alcohol), hydroxylethylcellulose, gum acacia, polyacrylic acid, and various other water-soluble polymers have been used a protective colloids for polymerization of various monomers. The use of poly(vinyl alcohol) for vinyl acetate polymers has been particularly important commercially. For example, see U.S. Pat. No. 3,708,388.
U.S. Pat. No. 4,335,220 describes the use of water-dispersible polyesters as sequestering agents for water-immiscible solids and liquids. The material to be dispersed must be a hydrophobic deformable organic substance.
U.S. Pat. No. 4,119,680 describes grafted water-dispersible copolyesters useful as binders and finishes for polyester containing fabrics. The polyesters contain .alpha.,.beta.-unsaturated dicarboxylic acids to provide sites for grafting. The graft copolymers are prepared by polymerization of vinyl or acrylic monomers in aqueous dispersions of these polyesters.
Water-soluble unsaturated polyester salts have been used to emulsify styrene to make polymers (Y. Ch. Chu and W. Funke, Angew. Makromol, Chem., 1982, No. 103, p. 187, 203; W. Funke et al., Makromol. Chem., 180, 1979, p. 2797; M. Narkis, J. Appl. Polym. Sci., 23, 1979, p. 2043; H. Baumann, B. Joos and W. Funke, Macromol. Chem. Phys., 1986, Vol. 187, p. 2933). This work concerns polyesters which are carboxyl terminated. The emulsifying properties are only observed if the carboxyl groups are completely dissociated, which requires a weakly alkaline environment (PH ca. 8.5). Work has been done with both saturated and unsaturated polyesters. These are low molecular weight polyesters with number average molecular weights reported from 1,000 to 3,000. At very short chain lengths the polyesters do not emulsify at all, and at higher molecular weights the polyesters are water insoluble even when the carboxyl groups are neutralized.
At the August 1987 national ACS meeting, a paper was presented by F. Cuirassier, Ch. H. Baradji and G. Riess on the preparation of microlatices in the presence of functionalized polyesters. The polyesters used were carboxy-terminated with number average molecular weights in the range of 1,000 to 4,000. Styrene and acrylic monomers were polymerized to form microemulsions. These polyesters appear to be similar to those used by Funke and are believed to have similar limitations.
Water-dispersible polyesters have found many applications in textile and printing applications. Water-dispersible polyesters have been used, for example, as textile sizes, particularly for polyester fibers, and have been used to develop aqueous inks. One characteristic of these water-dispersible polyesters is that the viscosity increases dramatically above about a 30% total solids content. As a consequence, these polyesters are typically used at solids content levels of 30% or less. Higher solids levels would be expected to offer several practical advantages including faster drying times and lower shipping and storage costs.
There exists a need for novel water-dispersible polyester blends and for an effective and practical way to prepare these polymer blends. There is also a need for a method of preparing aqueous dispersions of these polymer blends at total solids levels above 30% and preferably in the range of about 45% to 65% total solids. Finally, there is a need for a method of preparing water-dispersible polyester or polyesteramide blends which allows one to vary the properties of the polymer blend over a wide range of properties for each water-dispersible polyester or polyesteramide composition.